The present invention relates to a magnetic transfer method for transferring a recorded information to a magnetic recording medium used in a magnetic recording and reproducing system of large capacity and high recording density. In particular, the invention relates to a magnetic transfer method used in the recording of servo signal, address signal and other normal signal such as video signal, audio signal, data signal, etc. to a magnetic recording medium of large capacity and high recording density.
With rapid progress in the utilization of digital image, the amount of information to be handled in devices such as personal computer is now extensively increased. With the increase of the amount of information to be handled, there are now strong demands on a magnetic recording medium, which has large capacity for information recording and can be produced at low cost, and which requires shorter time for recording and reading.
In a high-density recording medium such as hard disk or large-capacity removable type magnetic recording medium such as ZIP (Iomega Inc.), information recording area has narrower tracks compared with floppy disk. In order that a magnetic head scans over tracks with narrow width and signals are recorded and reproduced at high S/N ratio, it is necessary to perform accurate scanning using tracking servo technique.
In this respect, in a large-capacity magnetic recording medium such as hard disk, removable type magnetic recording medium, etc., there are provided areas where servo signal for tracking, address information signal, reproduction clock signal, etc. are recorded at a given angular distance with respect to one turn of the disk. The magnetic head reproduces these signals at a given spacing and scans accurately over the tracks while confirming and correcting the position of the head. These signals are recorded on the magnetic recording medium in advance when the magnetic recording medium is manufactured, and it is called xe2x80x9cpre-formatxe2x80x9d.
Accurate positioning is required for the recording of servo signal for tracking, address information signal, reproduction clock signal, etc., and the pre-format recording is generally practiced by the magnetic head under strict position control using a special-purpose servo recording system after the magnetic recording medium has been incorporated in the drive.
However, in the pre-format recording of servo signals, address information signal, reproduction clock signal, etc. by the magnetic head, recording is performed under strict position control of the magnetic head using a special-purpose servo recording system, and recording is performed one by one and track by track. Thus, long time is required for the pre-format recording. Also, with rapid increase of magnetic recording density, the amount of signals to be recorded in the pre-format recording is increased, and this means that still more time is required. The cost required for the pre-format recording process of signals such as servo signal in total manufacturing cost is increased in the production of the magnetic recording medium, and there are now strong demands on the reduction of the cost in this process.
On the other hand, a method has been proposed, in which the pre-format information is not recorded track by track, but it is transferred from the master carrier to the slave medium by magnetic transfer. For instance, such transfer technique is described in JP-63183623(A), JP-10040544(A), (EP-0915456) and JP-10269566(A).
According to the method described in JP-10040544(A) or JP-10269566(A), convex and concave portions to correspond to information signals are formed on the surface of the substrate used as the master carrier for magnetic transfer. Ferromagnetic thin film is formed at least on the surface of the convex portions. The surface of this master carrier is brought into contact with the surface of a sheet-type or a disk-type magnetic recording medium where a coating layer containing ferromagnetic thin film or ferromagnetic power is formed. Or, AC bias magnetic field or DC magnetic field is applied, and the ferromagnetic material on the surface of convex portion is excited. As a result, magnetized pattern corresponding to convex and concave portion is recorded on the magnetic recording medium.
According to this method, the surface of convex portion of the master carrier for magnetic transfer is brought into close contact with the magnetic recording medium to be pre-formatted, i.e. the slave medium, and the ferromagnetic material in the convex portion is excited. Then, a given pre-format information is recorded on the slave medium. Static recording can be carried out without changing relative position of the master carrier for magnetic transfer and the slave medium. Accurate pre-format recording can be achieved, and the time required for the recording is very short.
In the magnetic transfer method as described above, the master carrier for magnetic transfer and the slave medium are brought into close contact with each other in static state, and magnetic transfer is performed. Therefore, damage occurs less frequently on the master carrier for magnetic transfer and the slave medium in the process of servo signal recording, and high durability can be expected in this method.
However, when the master carrier for magnetic transfer and the slave medium are brought into contact with each other and magnetic field is applied for magnetic transfer and this process is repeatedly carried out, signal dropout may occur. Thus, the signal recorded in the servo areas does not fulfill the function of the servo signal. As a matter of fact, this cannot be used as a magnetic recording medium.
After performing analysis on signal dropout, it was found that the signal dropout is usually caused due to poor adhesion between the master carrier for magnetic transfer and the slave medium.
It is an object of the present invention to provide a magnetic transfer method, by which it is possible to accurately transfer servo signal to the slave medium without resulting in dropout of some of the signal in a process to form servo areas on the slave medium. This is an indispensable process in the magnetic transfer from the master carrier to the slave medium and in the use of the slave medium as a large-capacity magnetic recording medium.
The above problems can be solved by the magnetic transfer method of the present invention. The present invention provides a magnetic transfer method for transferring information by bringing a master carrier for magnetic transfer and a slave medium into close contact with each other and by applying a magnetic field for transfer, the master carrier comprising servo areas and data areas, the servo areas are designed on convex form, and difference of height between the data area and the servo area is within the range of 50-800 nm.
The present invention also provides the magnetic transfer method as described above, wherein the master carrier for magnetic transfer has projections not higher than the height of the servo area and being disposed on the data area.